Laser shock peening (LSP), known as laser shot blasting, is a new material surface strengthening technique. LSP utilizes the mechanical effect of shock wave induced by strong laser to process the material, and features with high pressure, high energy, ultra-fast and ultra-high strain rate, etc. The residual compressive stress layer formed by LSP can effectively eliminate stress concentration in the material and inhibit occurrence and development of the crack, and thereby significantly improve the fatigue life and ability of corrosion resistance and wear resistance of metal parts.
At present, in China, LSP is mainly used for processing external surfaces of workpieces, such as blades and gears, but there are few reports on application of laser shock peening on bearings and parts that utilize a hidden surface as the working face. In the Chinese Patent Application No. 200610096476.5 filed by Yongkang ZHANG et al, titled as “Technical hole wall intensifying method based on laser impaction wave and apparatus”, a reflected shock wave processing method for hole walls of the workpiece is disclosed. Subsequently, in the Chinese Patent Application No. 201010510712.X filed by Yinfang JIANG et al, titled as “Method and device for laser shock processing of fastening holes”, a similar processing method for wall holes is disclosed. However, in a case that the hidden surface of the workpiece is a curved surface or the aperture size is large, both of the above-methods are not applicable. The reasons are: if the hidden surface of the workpiece is a curved surface, it will be difficult to produce an appropriate reflecting cone to enable the reflected shock wave act on the hidden surface uniformly; if the aperture size is very large, the reflected shock wave will tend to diffuse, and thereby the effect of laser shock peening on the hole wall will be compromised. The key point in the processing of a hidden surface is to introduce the laser beam into the workpiece and ensure an appropriate incident angle acts on the region to be processed of the hidden surface.